package leetcode.tree;

public class BalancedBinaryTree110 {
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode() {}
        TreeNode(int val) { this.val = val; }
        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    class Solution {
        public boolean isBalanced(TreeNode root) {
            return helper(root) != -1;
        }

        public int helper(TreeNode root) {
            if (root == null) {
                return 0;
            }
            int left = helper(root.left);
            int right = helper(root.right);
            if (left == -1 || right == -1 || Math.abs(left - right) > 1) {
                return -1;
            }
            return Math.max(left, right) + 1;
        }
    }
}
